The Bottom LineIf you thought dual cores were over the top, get ready. Intel presents the Core 2 Extreme QX6700, a single CPU with four distinct processing cores. At $999, the first quad-core CPU will remain an enthusiast part for a while, but as a glimpse of the future, it's clear that clock speed is out and core counts are in.

8.7 Overall

Design9.0

Features9.0

Performance8.0

Review Sections

Barely wrapped your brain around dual-core processors? It only gets worse from here, folks. Welcome to quad core, by way of Intel's Core 2 Extreme QX6700. Don't let the "Core 2" fool you (great job, Intel Product Naming department), this new chip has four physical processing cores in it that make it a multitasking beast. And if you're still stuck doing only one thing at a time on your desktop, the QX6700's promise for single-application performance is large, as well. We suspect that professionals and forward-looking gamers will be most interested in quad-core chips, and of the pros, the digital-media editors might not want to get rid of their Mac Pro's just yet. We found that with certain applications, Apple's high-end designer box is faster. At $999, the Core 2 Extreme QX6700 will likely end up in only the most expensive of desktops, but the fact is that the multicore revolution is fully upon us. You might not need a PC with such a pricey chip now, but our testing found that for applications and scenarios that will put it to the test, Intel's new quad-core chip will give you an absolute boost in performance.

We spared you the gory chip architecture details in our review of Intel's Core 2 Extreme X6800, and we're going to do the same here. The big news is doubling the number of cores to four; the rest of the chip architecture remains the same for the most part. If you must know all the ins and outs, we will refer you to our Alpha blog post that breaks down the bullet points. The key specs of the Core 2 Extreme QX6700 are its 2.66GHz-per-core clock speed, and its two separate 4MB L2 cache allotments--giving each pair of cores a 4MB pool to draw upon. That's, logically, twice as much cache as the dual-core Extreme X6800 chip. But if you've been paying attention to recent CPU developments, you might remember that the X6800 actually has a faster clock speed, coming in at 2.93GHz. Here's where multicore CPUs start to complicate our understanding of desktop processors.

If you'll recall, both Intel and AMD have been laying the groundwork to get people away from thinking of raw megahertz as the primary indicator of processor capability. The reason in a word is heat: The faster a chip runs, the hotter it becomes. When those Pentium Extreme Edition chips started hitting 3.6GHz and higher, the cumbersome liquid-cooling hardware required to keep them from overheating became a visible, noisy reminder that heat dissipation is a major challenge for system builders. Both AMD and Intel knew this before the Extreme Edition chips came to market, of course, but with the quad-core Core 2 Extreme QX6700, the answer to the problem becomes much easier to understand than even with dual-core CPUs; rather than make the chips faster, Intel has made them able to do more things at once.

Thus, we have four processing cores, each running at 2.66GHz. You have to be able to tap into all of the cores to see a difference in performance, which is why dual-core and multicore CPUs really shine on multitasking tests. So when would you ever be doing so many things at once on a computer? What about if you wanted to burn a DVD, listen to music, and edit a photo all at the same time? Another scenario we like is playing a game on your PC while someone in another room is using that same computer to stream digital media across your home network. If you tried doing those things with a fast, single-core CPU, you'd have to trade off CPU cycles, and your performance would suffer. But with a quad-core chip, in which each core is almost as fast as one single-core processor, suddenly your options increase.

So that's multitasking. What about when you're doing just one thing at a time? That's where multithreaded applications come in. When a program can tap into multiple cores on a single CPU, it's called a multithreaded application. Games are actually a great example of how multithreaded software can benefit. It's easy to understand that when you're playing a game, the graphics processing goes out to the 3D chip and the sound effects go through an audio chip, but what about artificial intelligence? Or physics calculations? Or dynamic scenery generation that creates new environments on the fly? Now what about doing all of those things at once? That's where a multicore chip can give you a benefit. The same goes for any application that involves running more than one process--applying multiple photo filters, encoding audio and video onto a DVD, the list goes on. Many popular applications such as Photoshop and iTunes already support multiple processing threads. You can also expect that more and more programs will ship with multithreaded code.

If you're wondering what kind of performance increase you can expect from the Core 2 Extreme QX6700, we saw dramatic speed increases with multitasking and multithreaded applications compared to Intel's Core 2 Duo Extreme X6800 and AMD's AMD Athlon 64 FX-62--the fastest dual-core chips Intel and AMD had to offer, respectively. Apple's Mac Pro, however, presents a different story. Our Apple test bed (a different system than the one we reviewed back in August) has two dual-core Xeon 5160 chips, each running at 3.0GHz. That makes its raw CPU speed faster than that of the Core 2 Extreme QX6700. On some of our apps--iTunes and Photoshop in particular--differences between running the programs on Windows XP and Apple OS X likely impact performance, but it's worth noting that even with a slower hard drive, the Mac Pro outpaced the Core 2 Extreme QX6700 chip on a number of tests, likely due to its clock speed advantage.

It seems to us that the performance takeaway is that for Windows users who can afford it, the Core 2 Extreme QX6700 is the way to go for the fastest PC today. As our single-core CineBench scores show, you might run into some apps that benefit more from raw clock speed than having multiple cores, but in general, we haven't seen a faster desktop chip. But professionals who have the luxury to choose among platforms are probably better off sticking with a Mac Pro, all other things being equal. We imagine that due to its partnership with Intel, Apple will be updating the CPUs in its high-end desktop in the near future, so it's not hard to fathom a Mac Pro with a single quad-core chip or perhaps two quad-core chips, so just because the current two dual-core Xeon design isn't quite a true "quad-core CPU," Mac loyalists shouldn't feel like they're limiting themselves.

But say you wanted to build your own quad-core PC. You won't be able to purchase the Core 2 Extreme QX6700 until November 14, and on that date, you'll also have to decide between building one on your own and buying one from Dell, Gateway, Velocity Micro, or any of the other typically high-end PC vendors. If you do go it alone, you'll need an Intel 975XBX2-based motherboard. As the company did with the original Core 2 Duo chips, we expect that Nvidia will have a compatible motherboard chipset for sale as well, but as of November 1, it hadn't announced anything. Neither Intel's nor Nvidia's previous Core 2 Duo-supporting chipsets are compatible with the Core 2 Extreme QX6700, so if you recently purchased such a motherboard, you'll need to upgrade. Memory support officially includes 533MHz and 667MHz DDR2 SDRAM, with unofficial support for faster 800MHz DDR2 RAM.